Question

What is a peptide bond? Explain with an example.

Hint:

Proteins are essentially long chains of amino acids linked together by peptide bonds. This is a dehydration synthesis reaction (condensation).

Answer 1

Definition:
A peptide bond is a chemical bond formed between two amino acid molecules when the carboxyl group ($-COOH$) of one amino acid reacts with the amino group ($-NH_2$) of another, releasing a molecule of water ($H_2O$). It is an amide linkage ($-CO-NH-$). Explanation with Example:
Consider the formation of a dipeptide Glycylalanine (Gly-Ala) from Glycine and Alanine.

• Glycine: $H_2N-CH_2-COOH$
• Alanine: $H_2N-CH(CH_3)-COOH$

Reaction: \[ H_2N-CH_2-COOH + H_2N-CH(CH_3)-COOH \xrightarrow{-H_2O} H_2N-CH_2-\mathbf{CO-NH}-CH(CH_3)-COOH \] Here, the $-\mathbf{CO-NH}-$ linkage connecting the two amino acid residues is the Peptide Bond.